Modern telecommunication technologies require high performance electronic circuits to operate according to customer or market needs. For example, telecommunication applications such as asymmetrical subscriber lines (ADSL), cable modem, and video applications may be required to provide error free or near error free data with minimum latency to an end user. Usually, electronic circuits used in these applications meet specifications with stringent requirements to perform these types of services.
Likewise, telecommunication applications that deliver voice services, such as cellular telephone services, may require a certain level of signal clarity. However, many radio frequency (RF) electronic circuits used in a cellular telephone application may create distortion that decreases signal clarity as well as quality of service of cellular telephone applications.
Many times, RF electronic circuits include transistors or other electronic devices that exhibit both linear and nonlinear characteristics, and at times, the nonlinear characteristics may create distortion. An electronic system has a linear characteristic, for example, if a voltage output is proportional to a voltage input. However, a system exhibits nonlinear characteristics if an output is not proportional to an input. That is, a nonlinear system cannot be described using variables written in a linear combination of independent components. Instead, a nonlinear electronic system may have an output that is proportional the square and/or cube of the input. Examples of nonlinear electronic devices include diodes and transistors that provide nonlinear current/voltage (UV) characteristics.
Some electronic circuits, such as amplifiers, not only increase an amplitude of signals at an operating frequency (e.g., ω), but also exhibit nonlinearity such that the amplifiers create spurious electronic signals that are multiples or harmonics of the operating frequency ω1. Such spurious electronic signals (or harmonics) may be referred to as distortion.
In a cellular telephone system, for example, a cellular phone may receive and deliver voice service using a certain frequency within a frequency range or frequency band. Other cellular users may receive and deliver their own voice service in adjacent frequency bands. For example, a cellular application used by one user may specify that operating frequency ω1 should be within a frequency range ωA-ωB while another cellular user may be using an application at another operating frequency within an adjacent frequency range ωB-ωC. Distortion components may be introduced in the adjacent frequency bands (i.e., ωB-ωC) and may create interference or decrease quality of signals used by cellular users due to closeness of frequency bands. Therefore, such telecommunication applications may require electronic circuits to minimize nonlinear characteristics so as to minimize distortion.